The packaging of semiconductor devices is conventionally carried out, whether in plastic or in ceramic packages, after the active circuit elements have been formed by semiconductor device processing. Individual circuits or groups of circuits are broken into so-called dice. The dice are then attached to lead frames. Bond pads on each die are bonded to the leads of the lead frame and the wired bonded lead frame and die are packaged. Such individual handling of dice in the fabrication of the devices is labor-intensive and thus undesirable.
High speed semiconductor devices often use air bridges to decrease the capacitance between metal lines and the silicon substrate. Air is an excellent dielectric and it is desirable to dispose air bridges between metal lines carrying high speed signals and the substrate.
While semiconductor devices are very small devices, miniaturization thereof is desirable but is adversely affected by the need to package the devices in a way that will protect them from damage or contamination. While encapsulation in plastic or ceramic provides suitable protection and isolation from contamination, the plastic or ceramic package is often many times the size of the semiconductor device and limits miniaturization thereof. In addition, plastic encapsulation may fill voids in the device, particularly voids that are provided for air bridges. The filling of these voids with plastic, which has a dielectric constant greater than air, increases the parasitic capacitance of the device and reduces its high frequency response limiting the speed at which signals can propagate in the device. Similar limitations exist where other devices, such as micromachines or machinable components, are needed.